1. Field of the Invention
The present invention relates to a lateral pressure mechanism for a motor which is used in a rotary driving device for a CD (Compact Disk) or the like.
2. Related Art
As a motor which is used in a rotary driving device for a CD or the like, known is a motor of the shaft rotation type in which a rotor case having a mounting unit for a disk, and a rotary shaft elongating from the rotor case are rotatably supported via a bearing on a motor frame. In such a motor of the shaft rotation type, a sintered oil-impregnated bearing which is more economical than a ball bearing and in which high-speed rotation is enabled is often used. A motor which uses a slide bearing such as a sintered oil-impregnated bearing must be configured so that a clearance is adequately formed between the inner peripheral surface of the bearing and the outer peripheral surface of a rotary shaft in order to allow the rotary shaft to smoothly rotate in the bearing. However, this clearance produces rattling in the rotary shaft, whereby the motor is caused to vibrate when it is driven.
To comply with the above, in a motor 1B shown in FIG. 5(a), a lateral pressure mechanism is configured in which one end of a coil spring 91 is attached to an apparatus 93 on which the motor 1B is mounted, and the other end is connected via an engagement hook 92 to the rotary shaft 50 of the motor 1B, whereby a rotary shaft 50 is pulled in a direction (the direction of the arrow A) which is substantially perpendicular to the axis L of the shaft. When a lateral pressure is applied to the rotary shaft 50 in this way, the outer peripheral surface of the rotary shaft 50 is forcedly pressed against one place of the inner peripheral surface of the bearing. Therefore, the rotary shaft 50 is prevented from rattling.
In a motor 1C shown in FIG. 5(b), a stator core 46 is formed into a shape which is asymmetric with respect to the rotary shaft 50. When the stator core is formed in this way, the magnetic attraction force of a rotor magnet 56 which is applied to the stator core 46 is unbalanced, and hence a rotor case 52 is inclined as indicated by the arrow B. As a result, the rotary shaft 50 is pressed against one place of the inner peripheral surface of the bearing. Therefore, the rotary shaft 50 is prevented from rattling.
In a motor 1D shown in FIG. 5(c), a magnet 94 is additionally disposed in one place of the upper face of a stator core 46. Also in this configuration, a rotor case 52 is inclined because the magnet 94 magnetically attracts the rotor case 52 as indicated by the arrow C. Consequently, the rotary shaft 50 is pressed against one place of the inner peripheral surface of the bearing. Therefore, the rotary shaft 50 is prevented from rattling.
However, the motor 1B having the lateral pressure mechanism which pulls the rotary shaft 50 by using the coil spring 91 as shown in FIG. 5(a) requires a space for disposing the coil spring 91 and the hook 92 outside the motor 1B. This impedes miniaturization and thinning of the apparatus 93 using the motor 1B. Even if the lateral pressure mechanism is to be disposed inside the motor 1B, the coil spring 91 must be disposed in a stretched state in order to attain a sufficient lateral pressure. Consequently, it is difficult to ensure a space for disposing the coil spring 91 in such a state, inside the small motor 1B.
In the motors 1C and 1D having a structure which uses a magnetic attraction force as shown in FIGS. 5(b) and 5(c), when the outer diameter of the rotor case 52 is reduced as a result of miniaturization, the portion which is to be magnetically attracted becomes closer to the rotary shaft 50. Therefore, the moment of the magnetic attraction force about the rotary shaft 50 is reduced, so that the rotor case 52 is hardly inclined. When the shape of the stator core is changed or a magnet for attraction is added as in the case of the motors 1C and 1D, the magnetic circuit is unbalanced, thereby producing a problem in that cogging occurs and the rotor case 52 cannot smoothly rotate.